The present invention is particularly applicable to inductively heating and quench hardening cylinder liners used in internal combustion engines or other thin walled workpieces having a constant circular cross section along their axis and will be described with particular reference thereto; however, the invention has broader applications and may be used for heating the interior surface of any bore of generally constant cross-section irrespective of the shape.
It is common practice to harden the inner cylindrical surface of various bores, such as cylinder liners, by using a circular inductor having an outside diameter slightly smaller than the diameter of the inner surface of the liner. The inductor is energized and moved or progressed upwardly along the cylindrical surface to progressively heat the surface by induction. A quenching mechanism is provided which follows below the inductor and directs a quenching liquid outwardly to quench harden the previously heated portions of the cylindrical surface. Often, the workpiece is rotated during this operation to assure a more uniform heating pattern.
Positioning of the inductor in such induction heating processes is important in that a uniform small gap must be maintained between the inductor and the surface being heated to assure uniform induction heating around the entire periphery of the surface.
In the past, the induction heating of cylinder liners for internal combustion engines, i.e. diesel engines, employed induction heating equipment included an inductor assembly having a large, strong, complex, laminate mandrel integrally supporting an inductor coil, a following quench ring assembly, large vertical hollow conductors supplying electrical current and cooling water to the inductor coil and a vertical tube feeding quench fluid to the quench ring assembly. These components were all permanently assembled into a unit. Each element of this inductor assembly or unit was a complex, expensive part, all of which were brazed together. The strength and complexity of the supporting mandrel and the structural integrity of the assembly were required in order to maintain rigidity and proper positioning of the inductor coil and to assure proper induction heating of cylinder liners by maintaining an accurate fixed air gap around the coil.
In the past, such induction heating units were made for a single diameter liner and they could not be segregated into easily separate components which would allow for interchangeability. This was not a problem in high volume dedicated application. Each machine was tailor-made for a given cylinder liner and the development costs were absorbed over the lifetime of the production run. It was believed that each inductor had to be specially designed and tested for a given liner.
With more competition in the equipment field and the introduction of low inventory, versatile manufacturing techniques, such as the "just on time" low inventory technique, into the automotive industry, it has been found that customers cannot or will not purchase a special machine for each size cylinder liners. Versatile manufacturing equipment is in demand. This presents serious problems. To solve this problem I found that I could design a mandrel with a replaceable inductor module and by changing only the inductor module, I could get acceptable results for various sized liners. To do this, I had to invent a positive positioning structure easily, precisely and rigidly interlocking any of several inductor modules of different size to a single mandrel. The positioning structure had to be easily understood and used by machine operators and easily connected to standard supplies of electric power and cooling and quench fluid. More importantly, the positioning structure had to precisely align the inductor coil of any of a number of inductor modules with the center line of the mandrel so that an induction heating machine could be changed to process liners of a different diameter by simply changing the inductor module without redesigning and realigning the entire machine.
The present invention provides a new and improved apparatus for induction heating bores, such as cylinder liners, which apparatus overcomes all of the above referred to problems and others and provides for the induction heating of bores of different diameters without the problems mentioned above.